This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No(s). 2002-100239 filed in JAPAN on Apr. 2, 2002, which is (are) herein incorporated by reference.
The present invention relates to a method and apparatus for detecting decrease in tire air-pressure, and a program for judging decompression of a tire. More particularly, it relates to a method and apparatus for detecting decrease in tire air-pressure, and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of both front wheels or rear wheels.
There has been conventionally known an apparatus for detecting decrease in tire air-pressure (DWS) in which decompression of a tire is detected on the basis of rotational (wheel speed) information of four wheel tires attached to a vehicle. Such an apparatus employs a theory that a rotational velocity or a rotational angular velocity of a compressed tire is increased when compared to remaining normal tires owing to a decrease in outer diameter (dynamic load radius of the tire) from that of a tire of normal internal pressure. In a method for detecting decrease in internal pressure on the basis of a relative difference in rotational angular velocities of tires (reference should be made to Japanese Unexamined Patent Publication No. 305011/1988),
DEL={(F1+F4)/2xe2x88x92(F2+F3)/2}/{(F1+F2+F3+F4)/4}xc3x97100 (%) 
is employed as a judged value DEL. Here, F1 to F4 denote rotational angular velocities of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
Since the tires are manufactured to include variations (initial differences) within standards, effective rolling radii of the respective tires are not necessarily identical with each other even though all of the tires are at normal internal pressure. This will result in variations in the rotational angular velocities of the respective tires. To cope with this point, there is proposed a technique in, for instance, Japanese Unexamined Patent Publication No. 206460/1998, in which initial correction coefficients for eliminating differences in effective rolling radii affecting rotational angular velocities are obtained whereupon the velocities of the respective tires are corrected by using such initial correction coefficients so as to perform judgment of decompression of tires on the basis of the judged values DEL.
However, since decompression is judged on the basis of a difference in sums of rotational angular velocities of the four wheels that are respectively located diagonally with respect to each other, it is impossible to simultaneously detect decompression of both front wheels or both rear wheels. It therefore exists the danger that fuel consumption is worsened through increase in rolling resistance of the tire and that a burst might be caused upon continuing running without being aware of decompression.
In view of the above facts, it is an object of the present invention to provide a method and apparatus for detecting decrease in tire air-pressure, and a program for judging decompression of a tire with which it is possible to detect simultaneous decompression of both front wheels or both rear wheels.
In accordance with a first aspect of the present invention, there is provided a method for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The method includes the steps of: detecting and storing rotational information of the respective tires; calculating and storing a slip rate; calculating and storing a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between right and left front tires, a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between right and left rear tires and a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between front tires and rear tires; comparing a correction coefficient between front tires and rear tires obtained from rotational information which are gained from tires attached to the vehicle when performing cornering running other than freewheeling with a correction coefficient between the front tires and the rear tires preliminarily obtained when at normal internal pressure; and judging simultaneous decompression of two wheel tires of both front wheels or simultaneous decompression of two wheel tires of both rear wheels on the basis of a relationship between a value obtained through comparison of the two correction coefficients and a specified threshold.
In accordance with a second aspect of the present invention, there is provided an apparatus for detecting decrease in tire air-pressure in which decrease in internal pressure of a tire is detected on the basis of rotational information obtained from tires attached to a vehicle. The apparatus includes: rotational information detecting means which detects the rotational information of the respective tires; rotational information storing means which stores the rotational information of the respective tires; slip rate calculating and storing means which calculates and stores a slip rate; correction coefficient calculating and storing means which calculates and stores a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between right and left front tires, a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between right and left rear tires and a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between front tires and rear tires; comparing means which compares a correction coefficient between front tires and rear tires obtained from rotational information which are gained from tires attached to the vehicle when performing cornering running other than freewheeling with a correction coefficient between the front tires and the rear tires preliminarily obtained when at normal internal pressure; and decompression judging means which judges simultaneous decompression of two wheel tires of both front wheels or simultaneous decompression of two wheel tires of both rear wheels on the basis of a relationship between a value obtained through comparison of the two correction coefficients and a specified threshold.
In accordance with a third aspect of the present invention, there is provided a program for judging decompression of a tire, in which for judging decrease in air-pressure of a tire, a computer is made to function as rotational information storing means which stores the rotational information of the respective tires; slip rate calculating and storing means which calculates and stores the slip rate; correction coefficient calculating and storing means which calculates and stores a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between right and left front tires, a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between right and left rear tires and a correction coefficient for correcting a difference in effective rolling radii owing to initial differences between front tires and rear tires; comparing means which compares a correction coefficient between front tires and rear tires obtained from rotational information which are gained from tires attached to the vehicle when performing cornering running other than freewheeling with a correction coefficient between the front tires and the rear tires preliminarily obtained when at normal internal pressure; and decompression judging means which judges simultaneous decompression of two wheel tires of both front wheels or simultaneous decompression of two wheel tires of both rear wheels on the basis of a relationship between a value obtained through comparison of the two correction coefficients and a specified threshold.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.